OC022: Quality control in the measurement of nuchal translucency in the first trimester of pregnancy

Abstract

Convergent enantioselective syntheses of angucyclinone‐type natural products rubiginones A2 (2) and C2 (1) and their 11‐methoxy regioisomers 3 a and 3 b have been achieved by using two domino processes from a common enantiomerically pure 1‐vinylcyclohexene 4. Key steps in the synthesis of this diene were the stereoselective conjugate addition of AlMe3 on (SS)‐[(p‐tolylsulfinyl)methyl]‐p‐quinol (9) and the elimination of the β‐hydroxy sulfoxide fragment, after oxidation to sulfone, to recover a carbonyl group. The first domino sequence comprised Diels–Alder reaction with a sulfinyl naphthoquinone followed by sulfoxide elimination. An efficient opposite regioselection in the cycloaddition step was achieved in the convergent construction of the tetracyclic skeleton using a sulfoxide at C‐2 or C‐3 of the dienophiles 5 or 6, derived from 5‐methoxy‐1,4‐naphthoquinone. The second domino process, triggered by oxygen and sunlight, allowed the transformation of the initial tetracyclic adducts into the final products after B ring aromatization, silyl deprotection and C‐1 oxidation.